Precision micro-hole for extended life batteries

ABSTRACT

Various embodiments of the invention provide an enclosure for a metal-air battery assembly for an extended wear hearing aid. The enclosure includes a diffusion control element having a dimensional property configured for controlling oxygen and moisture diffusion into the metal-air battery assembly to maintain a minimum battery voltage when the hearing aid is operating and worn in an ear canal of a user over an extended period. In an embodiment, the enclosure can comprise a shell with a base end having an opening therein forming a cavity within the shell and a base cap for covering the opening of the base end. A diffusion element is disposed on the base cap. In an embodiment, the diffusion element comprises a laser drilled precision micro hole having an aspect ratio of least about four and a diameter in the range of about 10 to 15 microns.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/945,149, filed on Nov. 26, 2007 (now U.S. Pat. No. 8,068,630), whichis a continuation of U.S. application Ser. No. 11/044,993, filed on Jan.26, 2005 (now U.S. Pat. No. 7,379,555), which claims the benefit ofpriority of U.S. Provisional Application No. 60/539,947, filed on Jan.28, 2004. U.S. application Ser. No. 11/044,993 is also acontinuation-in-part of U.S. application Ser. No. 10/052,199, filed onJan. 16, 2002 (now U.S. Pat. No. 7,215,789), which is a continuation ofU.S. application Ser. No. 09/327,717 (now U.S. Pat. No. 6,473,513),filed on Jun. 8, 1999, the full disclosures of each of which areincorporated herein by reference. This application is also related toU.S. Pat. No. 6,567,527, filed Aug. 7, 2000, the full disclosure ofwhich is incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

Embodiments of the invention relate to components for extending the lifeof metal air batteries. More specifically, the invention provides abattery enclosure and method for improving the performance of metal airbatteries used in extended wear hearing aids.

Since many hearing aid devices are adapted to be fit into the ear canal,a brief description of the anatomy of the ear canal will now bepresented. While, the shape and structure, or morphology, of the earcanal can vary from person to person, certain characteristics are commonto all individuals. Referring now to FIGS. 1-2, the external acousticmeatus (ear canal) is generally narrow and contoured as shown in thecoronal view in FIG. 1. The ear canal 10 is approximately 25 mm inlength from the canal aperture 17 to the center of the tympanic membrane18 (eardrum). The lateral part (away from the tympanic membrane) of theear canal, a cartilaginous region 11, is relatively soft due to theunderlying cartilaginous tissue. The cartilaginous region 11 of the earcanal 10 deforms and moves in response to the mandibular (jaw) motions,which occur during talking, yawning, chewing, etc. The medial (towardsthe tympanic membrane) part, a bony region 13 proximal to the tympanicmembrane, is rigid due to the underlying bony tissue. The skin 14 in thebony region 13 is thin (relative to the skin 16 in the cartilaginousregion) and is more sensitive to touch or pressure. There is acharacteristic bend 15 that roughly occurs at the bony-cartilaginousjunction 19 (referred to herein as the bony junction), which separatesthe cartilaginous 11 and the bony 13 regions. The magnitude of this bendvaries among individuals.

The ear canal 10 terminates medially with the tympanic membrane 18.Laterally and external to the ear canal is the concha cavity 2 and theauricle 3, both also cartilaginous. The junction between the conchacavity 2 and the cartilaginous part 11 of the ear canal at the aperture17 is also defined by a characteristic bend 12 known as the first bendof the ear canal. Hair 5 and debris 4 in the ear canal are primarilypresent in the cartilaginous region 11. Physiologic debris includescerumen (earwax), sweat, decayed hair, and oils produced by the variousglands underneath the skin in the cartilaginous region. Non-physiologicdebris consists primarily of environmental particles that enter the earcanal. Canal debris is naturally extruded to the outside of the ear bythe process of lateral epithelial cell migration (see e.g., Ballachanda,The Human ear Canal, Singular Publishing, 1995, pp. 195). There is nocerumen production or hair in the bony part of the ear canal.

A cross-sectional view of the typical ear canal 10 (FIG. 2) revealsgenerally an oval shape and pointed inferiorly (lower side). The longdiameter (D_(L)) is along the vertical axis and the short diameter(D_(S)) is along the horizontal axis. These dimensions vary amongindividuals.

First generation hearing devices were primarily of the Behind-The-Ear(BTE) type. However they have been largely replaced by In-The-Canal(ITC) hearing devices are of which there are three types. In-The-Ear(ITE) devices rest primarily in the concha of the ear and have thedisadvantages of being fairly conspicuous to a bystander and relativelybulky to wear. Smaller ITC devices fit partially in the concha andpartially in the ear canal and are less visible but still leave asubstantial portion of the hearing device exposed.

Recently, Completely-In-The-Canal (CIC) hearing devices have come intogreater use. These devices fit deep within the ear canal and can beessentially hidden from view from the outside. In addition to theobvious cosmetic advantages, CIC hearing devices provide, they also haveseveral performance advantages that larger, externally mounted devicesdo not offer. Placing the hearing device deep within the ear canal andproximate to the tympanic membrane (ear drum) improves the frequencyresponse of the device, reduces distortion due to jaw extrusion, reducesthe occurrence of the occlusion effect and improves overall soundfidelity.

Many commercially available hearing aids, including CIC hearing aides,employ storage batteries including metal-air batteries as a powersource. The electrochemistry of these batteries requires oxygen in orderto generate current. Thus, for many hearings aids which have anenclosure surrounding the battery, a vent opening is necessary in orderto supply oxygen. However, the performance of metal-air hearing aidbatteries including that for vented hearing aids, can be adverselyeffected by either: 1) insufficient oxygen which shortens battery life;or 2) exposure to water and other liquids that wet the surface of thebattery, clog the vent holes and deprive the battery of oxygen. Thesefactor are problematic because many hearings aids, including CIChearings aids, are not readily removable by the user for periodicbattery replacement, should the battery stop functioning due to one orboth of the above causes.

One approach for limiting the oxygen and moisture flow into and out ofbatteries of the metal-air type includes the use of adiffusivity-limiting membrane (DLM) or a gas diffusion membrane (GDM).Such gas-diffusion membranes are typically comprised of one or morelayers of a compressed polymer material such as porouspolytetrafluoroethylene, such as Teflon® available from the DuPont®Corporation. See, for example, U.S. Pat. No. 4,189,526 to Cretzmeyer, etal., which uses a sintered polytetrafluoroethylene. However, one problemwith gas diffusion membranes such as PTFE is that the material is notdimensionally stable, that is it is easily stretched or otherwisedeformed. This makes it difficult to control one or more dimensionalparameters such as membrane thickness which affect the amount ofdiffusion through the membrane. This in turn, results in significantvariations in diffusion rates between different patches of membranewhich can result in oxygen starvation as well as flooding or drying ofthe battery electrolyte one or more of which can lead to shortenedbattery life. Consequently, diffusion of oxygen and moisture through gasdiffusion membranes such as PTFE can not be sufficiently controlled toallow production scale manufacturing of extended wear hearing aid metalair batteries. Thus, there is a need for a means to more preciselycontrol the ingress of oxygen and moisture into metal air batteries usedfor CIC and other extended wear hearing aids.

BRIEF SUMMARY OF THE INVENTION

Various embodiments of the invention provide systems, devices andmethods for improving the performance and reliability of metal airbatteries used for extended wear hearing aids including completely inthe canal hearing aids. Many embodiments provide an enclosure includinga diffusion control element for controlling oxygen and moisturediffusion into a battery assembly to improve one or more performanceparameters of the battery such as long term operation life of thebattery, operational capacity and the ability of the battery to maintaina minimum voltage when the hearing aid is in an operational mode andworn in the ear canal of a user over an extended period.

Many embodiments provide an enclosure for a metal-air battery assemblyfor an extended wear hearing aid. The enclosure includes a diffusioncontrol element having a dimensional property configured to controloxygen and moisture diffusion into the metal-air battery assembly tomaintain a minimum battery voltage when the hearing aid is operating andworn in an ear canal of a user over an extended period. This minimumvoltage is typically in the range from 1 to 1.3 Volts for batterycurrent drains in the range from about 40 to 175 μA with preferredranges of about 40 to 90 about 90 to 120 μA and about 120 to 175 μA. Inone embodiment, the enclosure can comprise a shell with a base endhaving an opening therein forming a cavity within the shell and a basecap for covering the opening of the base end with the diffusion elementdisposed on the base cap.

The diffusion control element is also configured to improve theoperational life of the battery by controlling the amount of moisturediffusion into the battery assembly within a range such that the batteryelectrolyte does not dry out nor does excessive moisture enter into thebattery assembly leading to condensation and flooding of the batteryassembly. By controlling both oxygen and moisture diffusion into thebattery assembly, various embodiments of the invention employing adiffusion control element allow for an in situ operation life of batteryof up to several months or longer.

In many embodiments, the diffusion control element will comprise one ormore precision micro though-holes which can be laser drilled. The shapeof the through-hole is desirably straight but it can also be curved,angled or otherwise non-linear and can comprise a combination of linearand non linear portions including curved portions. Desirably thethrough-hole has a length to diameter ratio (i.e. an aspect ratio) suchthat the gas ingress into the battery assembly is substantiallydiffusion controlled. In preferred embodiments, the aspect ratio will beabout four or greater with the diameter of the through-hole being nogreater than about 15 microns. Also in preferred embodiments, theportion of the enclosure including the micro-hole is fabricated from ametallized polymer such as a metallized PEEK. In an alternativeembodiment, this portion can be fabricated from a multilayer polymermaterial such that its bulk gas permeability is equal or less than ametallized polymer layer. That is, the imperfections in a single layercausing diffusion/permeability are blocked by the next overlying layer.

An exemplary embodiment of a method of using a hearing aid having abattery assembly with a diffusion control element comprises positioningthe hearing aid into the ear of a user and controlling air ingress intothe battery assembly to maintain a minimum battery voltage when thehearing aid draws current from the battery. Typically, the minimumvoltage will be in the range from about 1 to 1.3 Volts and the drawncurrent will be in the range from about 40 to 90 μA, but can range fromabout 40 to 120 μA, about 40 to 175 μA or about 1 to 175 μA.

In some embodiments the diffusion control element can comprise anon-compressed portion of a compressed gas porous membrane coupled to aportion of the enclosure. The compressed portion is sufficientlycompressed to significantly reduce the gas permeability of thecompressed portion relative to the un-compressed portion. The porousmembrane can include PTFE or other porous membrane known in the art. Forembodiments where the enclosure comprises a shell with a base cap, theporous membrane can be disposed on the base cap.

In other embodiments, the diffusion control element can include aregulator configured to regulate oxygen and moisture diffusion into themetal-air battery assembly responsive to a hearing aid parameter such asa user selected hearing aid volume, hearing aid operational mode (e.g.sleep vs. active mode), hearing aid gain, hearing aid frequency responseand the like. The regulator can include a valve or shutter, or a MEMSdevice which can have a valve, shutter or similar function

An exemplary embodiment of a method of using a hearing aid having abattery assembly with a regulator comprises positioning the hearing aidinto the ear of a user and regulating air ingress into the batteryassembly responsive to a hearing aid parameter such as a hearing aidgain, a hearing aid volume, or a user selected hearing aid volume.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side coronal view of the external ear canal.

FIG. 2 is a cross-sectional view of the ear canal in the cartilaginousregion.

FIG. 3 is a cross-sectional view illustrating an embodiment of a hearingaid device positioned in the bony portion of the ear canal.

FIG. 4A is a cross-sectional view illustrating an embodiment of ametal-air hearing aid battery assembly.

FIG. 4B is a cross-sectional view illustrating an embodiment of anenclosure for a hearing aid battery assembly.

FIG. 4C is a cross-sectional view illustrating an embodiment of ahearing aid battery enclosure having a multi-layer construction.

FIG. 5 is a perspective view illustrating an embodiment of a hearing aidbattery enclosure comprising a shell and a base cap, the base capincluding a diffusion control element.

FIG. 6 is a cross-sectional view illustrating an embodiment of theenclosure wall having a diffusion control element comprising amicro-hole.

FIG. 7 is a cross-sectional view illustrating an embodiment of theenclosure wall having an array of micro-holes.

FIGS. 8A-8C are cross-sectional views illustrating an embodiments of themicro-hole having different shapes including curved portions, curved andstraight portions, and curved and angled portions.

FIG. 9 is a cross-sectional view illustrating an embodiment of adiffusion control element comprising a gas permeable membrane.

FIG. 10A is a cross-sectional view illustrating an embodiment of thebattery enclosure including a regulator for regulating gas influx intothe battery assembly

FIG. 10B is block diagram illustrating use of the regulator forregulating gas influx into the battery enclosure responsive to one ormore inputs.

FIG. 11A is a graph of load in volts versus time in minutes for a seriesof batteries at a drain of 120 μA that have metallized, laser-drilledmicro holes according to an embodiment of the invention.

FIG. 11B is a graph of load in volts versus time in hours for a seriesof batteries at a drain of 120 μA that have metallized, laser-drilledmicro holes according to an embodiment of the invention.

FIG. 12 is a graph of load in volts versus time in minutes for a seriesof batteries at a drain of 175 μA that have metallized, laser-drilledmicro holes according to an embodiment of the invention.

FIG. 13 is a graph of load in volts versus time in minutes for a seriesof batteries at a drain of 200 μA that have metallized, laser-drilledmicro holes according to an embodiment of the invention.

FIG. 14 is a graph indicating battery life for a series of batteriesthat have metallized, laser-drilled micro holes according to anembodiment of the invention. The graph shows load in volts versusoperational life in days for batteries that were tested at threedifferent levels of humidity.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of the invention provide systems, assemblies andstructures for controlling the ingress of oxygen and water vapor intothe enclosures of metal air batteries used for CIC and other extendedwear hearing aids. Referring now to FIGS. 3-7, an embodiment of a CIChearing aid device 20 can include a microphone assembly 30, a receiveror speaker assembly 35 and a battery assembly 40 including a battery 50contained in battery cavity 60 by an enclosure 70. In variousembodiments, battery 50 can employ a variety of electrochemistry knownin the art including, but not limited to, lithium, lithium polymer,lithium ion, nickel cadmium, nickel metal hydride, or lead acid orcombinations thereof.

In preferred embodiments, battery 50 is a zinc-air or other metal-airbattery known in the art an embodiment of which is shown in FIG. 4A.Metal air battery 50 includes an air cathode assembly 51 and anodeassembly 52 and an enclosure 53. Air cathode assembly 50 representsseveral layers of active and passive materials known in the art ofbattery design. Anode assembly 52 includes anodic material 52 m which istypically made of amalgamated zinc powder with organic and inorganiccompounds including binders and corrosion inhibitors. Anodic material 52m also includes the electrolyte, typically an aqueous solution ofpotassium hydroxide (KOH) or sodium hydroxide (NaOH). Air (includingoxygen) reaches the cathode assembly from an air hole or aperture 54within the base of enclosure 53.

An embodiment of a battery enclosure 70 for controlling moisture andoxygen influx into battery assembly 40 is shown in FIG. 4B. Enclosure 70can be an enclosure for and/or a shell (part) of the battery. Theenclosure can include a diffusion control element 80 or other means ofcontrolling air ingress into the battery assembly. Desirably, all or aportion of enclosure 70 is fabricated from a gas impermeable material(including impermeability to oxygen and water vapor) such as a metal orgas impermeable polymer known in the art. Such embodiments enhance thecontrol of gas ingress into battery by limiting that ingress to thediffusion control element. In preferred embodiments, the walls 70 w ofat least a portion of the enclosure 70 are fabricated from a metallizedpolymer 71 and thus include a metal layer 72 and underlying polymerlayer 73. Suitable material for polymer layer 73 can include withoutlimitation, polyamides, polystyrenes and butyl rubber. In preferredembodiments, polymer layer 73 is PEEK (poly ether-ketone) or aco-polymer thereof. The polymer can be metallized using methods known inthe art (e.g. vacuum deposition, sputtering, etc). The metallizedpolymer 71 including diffusion control element 80 can in variousembodiments, be configured in one or more of the following fashions: i)form the base portion of enclosure 70; ii) be attached to an interiorsurface of enclosure 70, such as a base interior surface; iii) beincorporated as a patch under an existing battery aperture; or iv) beintegrated with the battery cathode assembly 51.

As shown in FIG. 4C, in an alternative embodiment, at least a portion ofthe enclosure can be fabricated from a multiple polymer layer orlaminate 74 that collectively has a gas permeability comparable to ametallized polymer layer. Laminate 74 can be fabricated from two or morepolymer layers 72 that are adhered or otherwise joined together to coverover any pinholes or other imperfections 72 c in a given layer whichserve as channels of increased gas permeability through a given layer.Suitable polymers for laminate 74 include polyamides known in the art.The layers can be joined using various polymer processing methods knownin the art (e.g. coating, co-extrusion, calendaring, etc.).

Referring now to FIG. 5, in many embodiments, the enclosure can comprisea shell 75 (also known as anode shell 75), with a shell opening 76 toshell cavity 77 and a base cap 78 which covers the base opening andseals the contents of battery assembly therein. Anode shell 75 can havecylindrical or other shape and can substantially oval cross section tocorrespond to that of a typical ear canal. As shown in FIG. 5, a batteryvent or micro-hole 90 (discussed herein) or other diffusion controlelement 80, can be disposed on base cap 78, typically on a centerportion of the base cap. In such embodiments, only base cap 78 need befabricated from a metallized polymer or other gas impermeable materialand the remainder of the shell can be fabricated from metal. Inpreferred embodiments, anode shell 75 is made of either a bi-clad ortri-clad material such as stainless-steel/copper ornickel/stainless-steel/copper. The stainless steel comprises most of thethickness of the shell and provides the structural support for theshell. The outermost layer is stainless-steel (bi-clad) or nickel(tri-clad), providing a high electrical conductivity surface. The insideof the shell is preferably made of oxygen free copper which forms asurface alloy inhibiting oxidation and reducing reactions with the zincinside the shell. The anode shell has a thickness of less than 0.2 mmand preferably in the range of about 0.1 to 0.16 mm.

In many embodiments, enclosure 70 includes a diffusion control element80 configured to control moisture and air influx into the batteryassembly 40 so as to improve battery performance and extend batteryoperational life for hearing aid 20 worn completely in ear canal 10. Invarious embodiments, diffusion control element 80 can comprise a hole, aporous or permeable membrane, valve, a shutter, or a MEMS device havinga valve, shutter or other related function. Referring now to FIG. 6, inpreferred embodiments, diffusion control element 80 comprises one ormicro through holes 90 (herein after micro-hole 90, also known aschannel 90). Micro-hole 90 has a diameter 90D and a length 90L. Invarious embodiments, diameter 90D can be in the range of about 10 to 15microns (μm), more preferably in the range of about 11 to 14 μm. Also,preferably, diameter 90D is no greater than 15 μm. In variousembodiments, micro-hole 90 is a precision micro-hole 90 p which canhave, for example, a diameter within 10% of a desired nominal value andmore preferably within 5%.

Micro-holes 90 and 90 p can be produced using a variety of machiningmethods known in the art such as micro drilling and other micromachining methods. In preferred embodiments, micro-holes 90 p are laserdrilled using laser drilling methods known in the art. Suitable lasersfor drilling include excimer and YAG lasers. Various laser parameterssuch as laser fluency, pulse repetition rate, scanning speed and focallength can be controlled to obtain the desired specifications andcharacteristics of the micro-hole (e.g. diameter, precision, aspectratio, diffusion rate, etc). Use of laser drilling allows for bothprecise hole diameter as well as production of less membrane debris. Formicro-hole arrays 91, the holes can drilled individually or gangdrilled.

The aspect ratio 90A of micro-hole 90, that is the ratio of length 90Lto diameter 90D can be selected so as to control the mass transfer ofair (including oxygen and water vapor) into and out of battery enclosure70. In preferred embodiments, the aspect ratio 90A is configured is suchthat essentially the only mode of mass transfer for air (includingoxygen and water vapor) into and out of enclosure 70 is via diffusion(i.e. convective mass transfer is essentially eliminated). Suchembodiments provide a diffusive channel 92 for precisely controlling gasinflux into the battery enclosure. Preferably, aspect ratio 90A isgreater than about 4. In one embodiment, this can be achieved by a holediameter 90D of less than about 15 μm and a hole length 90L of greaterthan about 45 μm. In other embodiments, the micro-hole can have adiameter of about 10 to about 15 μm and an aspect ratio greater thanabout 6.00 and more preferably a diameter from about 11 to about 14 μmand an aspect ratio greater than about 6.25. In a preferred embodiment,a micro-hole of about 12 μm was drilled in a 76 μm thick metallized PEEK(polyethyletherketone) sheet, giving rise to an aspect ratio greaterthan 6.3. The 12 micron hole was drilled into the metallized polymermaterial using an excimer laser.

In various embodiments, aspect ratio 90A can be further increasedthrough the use of multiple micro-holes 90 which can comprise amicro-hole array 91 as is shown in FIG. 7. For example, in oneembodiment shown in FIG. 7, three micro-holes 90 can be employed eachhaving a 5 μm diameter an 50 μm length. Use of multiple micro-holes withhigher aspect ratios provides enhanced diffusion into the enclosure,increased uniformity of gas concentration within the enclosure, as wellas hole redundancy while still maintaining control over water vapor andoxygen ingress into the enclosure.

The shape of the micro-hole 90 is desirably straight but in variousembodiments, can be angled, curved or otherwise non-linear and cancomprise a combination of linear and non-linear portions includingcurved portions. Referring now to FIGS. 8A-C, in an embodiment shown inFIG. 8A, micro-hole 90 can be curved, with a selectable radius ofcurvature. In an alternative embodiment shown in FIG. 8B, micro-hole 90can include a curved portion 90C and straight portion 90S. In stillanother alternative embodiment shown in FIG. 8C, hole 90 can include acombination of angled 90G and curved portions 90C in a-zig zag or otherpattern. Use of combinations of linear and non linear portions for themicro-hole can provide enhanced diffusion control of gas ingress byproviding a baffling effect as well as increasing the length of the holewithout having to increase the thickness 70T of enclosure 70. Also itreduces the risk of liquid (e.g. from condensed water vapor) fromentering into the battery enclosure and flooding the battery, thusproviding the battery with an enhanced means of liquid protection. Invarious embodiments, micro-holes having non-linear portions can beproduced using micro-drilling and other micromachining methods know inthe art. Alternatively, non linear micro-holes can be produced bymolding the battery enclosure (with the holes formed in the mold) usinginjection molding methods known in the art.

Referring now to FIG. 9, in alternative embodiments, portions ofenclosure 70 can comprise a membrane 100 including gas impermeableportions 110 and permeable portions 120, wherein the gas permeableportions comprise diffusion control element 80. In preferred embodimentsof a membrane based enclosure, membrane 100 comprise a porous membrane,portions of which have been sufficiently compressed to form impermeableportion 110, while still leaving a selected uncompressed portion to formpermeable portion 120. Specifically membrane 100 is sufficientlycompressed so as to occlude or otherwise reduce membrane pore size so asto significantly reduce gas permeability through the compressed portion.One or more permeable portions 120 can be positioned on membrane 100. Inpreferred embodiments, permeable portion(s) 120 is positioned in centerportion of membrane 100. In embodiments where enclosure 70 comprises ashell 75, membrane 100 can be used to fabricate all or portion of cap78, with permeable portion 120 centrally disposed on the cap. Thediameter of portions 120 is preferably in the range of about 10 to 15 μmand more preferably in a range of about 11 to 14 μm. By compressing themembrane to make it essentially impermeable to diffusion, and insteadusing the relatively small uncompressed portions to control diffusion tobattery the dimensional instability problems of the prior DLM membranesare overcome.

Permeable portion 120 can have variety of shapes including substantiallycircular, semicircular, or rectangular shaped. Suitable materials formembrane 100 can include polytetrafluoroethylene, such as Teflon®available from the DuPont® Corporation. The permeability/diffusion ratesthrough permeable and impermeable portions 110 and 120 can be measuredusing permeability/porosity measurement methods known in the art, forexample, liquid extrusion porosimetry or bubble point methods. Further,such methods can be used to calibrate the amount of compression for agiven type or even lot of membrane material. For example, lots having ahigher initial permeability/average pore size can be compressed to agreater amount than those having lower initial permeability/average poresizes.

Referring now to FIGS. 10A-10B, in various embodiments, diffusioncontrol element 80 can include a regulator 130 which regulates diffusioninto enclosure 70 in response to one or more inputs 135. Regulator 130can be positioned within micro-hole 90 or can be disposed within or onenclosure wall 70W such that the regulator itself forms a channel 90 forthe diffusion of gas into the enclosure. For embodiments using amembrane 100, regulator 130 can also be positioned in the membraneincluding in permeable portions 120. In various embodiments, regulator130 can comprise a valve, a shutter or a MEMs device which has ashutter, valve or similar function. Further, the MEMs device can be amechanical or electromechanical based device. The MEMs device can befabricated using MEMs fabrication methods known in the art such asphotolithographic methods. Also, regulator 130 can be formed within wall70W itself using MEMS, or other related processing methods. Example MEMsbased valves and flow controllers include those described in U.S. Pat.No. 6,149,123 which is fully incorporated by reference herein.

In various embodiment inputs 135 can include various hearing aidparameters including without limitation, hearing aid gain, frequencyresponse, volume, ambient noise levels and sound characteristics (e.g.voice vs. background sound) the operational mode of the hearing aid(e.g. active or standby) and the like. In a preferred embodiment input135 is an output or pre-amplified output from microphone assembly 30,and/or a pre-amplified input into receiver assembly 35. Also, inpreferred embodiments, regulator 130 regulates oxygen and moisturediffusion into the metal-air battery assembly responsive to a hearingaid volume which can be a user selected hearing aid volume. In use,regulator 130 provides a means for improving one more batteryperformance parameters by regulating the influx of oxygen responsive tothe electrical power requirements of the hearing aid.

In various embodiments, inputs 135 can be made: i) directly to regulator130, ii) to a controller 140 which sends a control signal 145 regulator130; or iii) to hearing aid 20. Controller 140 can be integral to orotherwise coupled to regulator 130. Controller 140 can also be integralto or otherwise coupled to hearing aid 20, can for example be coupled tothe hearing aid microphone, receiver or battery assemblies. Controller130 can be a microprocessor, a mechanical or electro-mechanicalcontroller, or a mechanical or electro-mechanical MEMS device which isincorporated regulator 130 for embodiments where regulator is a MEMS.

As discussed herein, micro-hole 90 can be configured to control bothoxygen and moisture (e.g., water vapor) influx into battery enclosure 70so as to improve one or more battery performance parameters. Suchparameters can include, but are not limited long term operational lifeof the battery when the hearing aid is operated in the ear canal and theability of the battery to maintain a minimum voltage of a user over anextended period. In terms of achieving the latter parameter, embodimentsof the enclosure can include a micro-hole with e an aspect ratioconfigured to supply sufficient oxygen influx to the battery assembly tomaintain a desired minimum battery voltage for a given current drain.This minimum voltage will typically be in the range from 1 to 1.3 Voltsfor battery current drains in the range from about 40 to 175 μA, withspecific ranges of about 40 to 90 μA, about 42 to 85 μA, about 90 to 120μA, about 120 to 175 μA and about 1 to 175 μA. In a specific embodimentthe current drain is about 42 μA. In various embodiments the aspectratio for maintaining such voltages can be between about 4 to 7 with apreferred embodiment of about 6.33. As shown in FIGS. 11-12 (See also,Examples), sample builds of battery enclosures with micro-holesfabricated in accordance with embodiments of the invention were morethan capable of meeting these parameters over an extended time period.

The operational life of metal air hearing aid batteries can be shortenedby the presence of either too much or too little moisture which causeelectrolyte materials in the battery cathode to either become flooded ordry out. Either condition can occur in the ear canal, particularly thelatter due to sweat and exposure to water from showering and swimming.Accordingly, improvements in the battery operational life in the earcanal can be achieved by embodiments of the micro-hole that have anaspect ratio configured to control the influx of moisture (in the formof water vapor) into the battery assembly so as to maintain the moisturelevel within the enclosure within an operational range such that 1) thecathode electrolyte does not dry out; and 2) excessive moisture does notenter into the battery assembly causing condensation and flooding of thebattery. In various embodiments, the aspect ratio for controllingmoisture influx to prevent these conditions can be between about 4 to 7with a preferred embodiment of about 6.33. As shown in FIG. 14 (Seealso, Examples), sample builds of battery enclosures with micro-holesbuilt in accordance with embodiments of the invention were able toachieve battery lives in excessive of 210 days when tested at 38° C. andrelative humidity as high as 60%.

EXAMPLES

Various embodiments of the invention will now be further illustratedwith reference to the following examples of metallized polymermembranes/battery enclosure assemblies constructed with a precisionmicro-hole. However, it will be appreciated that these examples arepresented for purposes of illustration and the invention is not to belimited by this specific examples or the details therein.

Example 1

A series of battery cells were fabricated that included enclosure havingmicro holes laser-drilled in a metallized PEEK (polyethyletherketone)sheet membrane. A micro-hole of about 12 microns was drilled in a 76micron (about 3 mil) thick PEEK (polyethyletherketone) sheet, givingrise to an aspect ratio greater than 6.3. The 12 micron hole was drilledusing an excimer laser. The batteries were tested for their ability tomaintain a minimum voltage at current of 120 μA and 175 μA. FIGS. 11A-12indicate that the samples were able to maintain voltage greater than 1.3Volts for periods of 60 minutes and or longer, while FIG. 11B indicatesthat the samples were able to maintain about this voltage for nearly 50hours. The flat voltage response indicates that the laser drilled holesallowed enough oxygen ingress to provide useable currents at either the120 μA or 175 μA or current drain levels. Experiments conducted at a 200μA current drain level produced a voltage response that continued in adownward direction and did not level out as compared to the responsecurves for the 120 μA or 175 μA current levels (See FIG. 13). Theincreased downward slope of the 200 μA curve indicates that the batteryis oxygen starved at this current. Such oxygen starvation at the 200 μAcurrent level in turn suggests that the micro-hole is properly limitingexcess oxygen influx at the 125 and 175 μA current levels.

Example 2

A series of 194 battery cells were fabricated that included enclosurehaving micro holes laser-drilled in a metallized PEEK(polyethyletherketone) sheet membrane. A micro-hole of about 12 micronswas drilled in a 76 micron (about 3 mil) thick PEEK(polyethyletherketone) sheet, giving rise to an aspect ratio greaterthan 6.3. The 12 micron hole was drilled using an excimer laser. Thebatteries were tested for battery life at 38° C. and relative humiditiesof 15, 40 and 60% at an current drains 33 μA (this represents an averagecurrent over a user day assuming 16 hours of on-time at 42 μA and 8hours of standby at 15 μA). Battery life was assessed by the ability tomaintain voltage above one volt. As FIG. 14 indicates, battery life ofthe samples ranged over 190 to over 210 days.

The foregoing description of various embodiments of the invention hasbeen presented for purposes of illustration and description. It is notintended to limit the invention to the precise forms disclosed. Manymodifications, variations and refinements will be apparent topractitioners skilled in the art. Further, the teachings of theinvention have broad application in the hearing aid device fields aswell as other fields which will be recognized by practitioners skilledin the art. For example, various embodiments of the invention can beadapted and used for metal air batteries in any number of applicationswhere it is desirable to control oxygen and moisture influx into abattery assembly, and/or to regulate oxygen influx in response to thepower demands put on the battery. Such applications can include, withoutlimitation, watches and calculators, portable electronics and medicalinstrumentation including portable and implantable instrumentation.

Elements, characteristics, or acts from one embodiment can be readilyrecombined or substituted with one or more elements, characteristics oracts from other embodiments to form numerous additional embodimentswithin the scope of the invention. Hence, the scope of the presentinvention is not limited to the specifics of the exemplary embodiment,but is instead limited solely by the appended claims.

What is claimed is:
 1. An enclosure for a metal-air battery assembly foran extended wear hearing aid, the enclosure including a diffusioncontrol element having a dimensional property configured for controllingoxygen and moisture diffusion into the metal-air battery assembly tomaintain a minimum battery voltage when the hearing aid is operating andworn in an ear canal of a user over an extended period, wherein theenclosure comprises a metal shell having at least one hole and whereinthe diffusion control element comprises a polymer layer having aprecision micro-hole formed therein and being arranged in series withthe hole in the shell to control oxygen and moisture diffusion.
 2. Theenclosure of claim 1, wherein the shell comprises a base end having anopening therein forming a cavity within the shell and a base cap forcovering the opening of the base end.
 3. The enclosure of claim 2,wherein the at least one hole in the shell is disposed in the base capand the polymer layer is laminated to the base cap with the micro-holealigned with the hole in the cap.
 4. The enclosure of claim 1, whereinthe minimum battery voltage is in a range from about 1 volt to 1.3Volts.
 5. The enclosure of claim 1, wherein a current drain at which theminimum voltage is maintained is in range from about 40 μA to 175 μA. 6.The enclosure of claim 5, wherein a current drain at which the minimumvoltage is maintained is in range from about 40 μA to 90 μA.
 7. Theenclosure of claim 1, wherein the diffusion control element isconfigured to control moisture diffusion into the battery assembly tomaintain a battery electrolyte concentration within a range sufficientto allow the battery to power the hearing aid.
 8. The enclosure of claim1, wherein at least a portion of the micro-hole is curved or non-linear.9. The enclosure of claim 1, wherein the micro-hole is laser drilled.10. The enclosure of claim 1, wherein the micro-hole has a length todiameter ratio such that the gas ingress into the battery assembly issubstantially diffusion controlled.
 11. The enclosure of claim 10,wherein the micro-hole has a length to diameter ratio of at least about4.
 12. The enclosure of claim 1, wherein the precision micro-hole in thepolymer layer has a diameter not greater than about 15 microns.
 13. Theenclosure of claim 1, wherein the polymer layer has a plurality ofprecision micro-holes.
 14. The enclosure of claim 1, wherein the polymerlayer and the metal shell comprise a metallized polymer.
 15. Anenclosure for a metal-air battery assembly for an extended wear hearingaid, the enclosure comprising: a metal shell having at least one shellhole; and a diffusion control system, arranged in series with the shellhole, to control gas diffusion into the metal-air battery assembly,including a precision micro-hole, and a gas flow regulator associatedwith the precision micro-hole and configured to regulate diffusionthrough the micro-hole as a function of a hearing aid parameter when thehearing aid is operating and worn in an ear canal of a user over anextended period.
 16. An enclosure as claimed in claim 15, wherein themetal shell comprises a base end having an opening therein forming acavity within the shell and a base cap for covering the opening of thebase end.
 17. An enclosure as claimed in claim 15, wherein the gas flowregulator is located within the micro-hole.
 18. An enclosure as claimedin claim 15, wherein the gas flow regulator defines the micro-hole. 19.An enclosure as claimed in claim 15, wherein the gas flow regulatorincludes a shutter or a valve.
 20. An enclosure as claimed in claim 15,wherein the gas flow regulator includes a MEMS device.
 21. An enclosureas claimed in claim 15, wherein the hearing aid parameter is selectedfrom the group consisting of hearing aid gain, frequency response,volume, ambient noise levels, sound characteristics, hearing aidoperational mode.
 22. An enclosure as claimed in claim 15, wherein thehearing aid parameter comprises one or more of an output from amicrophone assembly, a pre-amplified output from the microphoneassembly, and a pre-amplified input into a receiver assembly.
 23. Anenclosure as claimed in claim 15, wherein the gas flow regulator isconfigured to regulate oxygen and moisture diffusion into the metal-airbattery assembly.
 24. An enclosure as claimed in claim 23, wherein thehearing aid parameter comprises volume.
 25. An enclosure as claimed inclaim 15, wherein the gas flow regulator is configured to regulateoxygen and moisture diffusion into the metal-air battery assembly tomaintain a minimum battery voltage.